drivers/rtc/rtc-ds1672.c: convert struct i2c_msg initialization to C99 format

Convert the struct i2c_msg initialization to C99 format.  This makes
maintaining and editing the code simpler.  Also helps once other fields
like transferred are added in future.

Signed-off-by: Shubhrajyoti D <shubhrajyoti@ti.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>